The invention relates to a multilayer foil composite which has at least one layer composed of polycarbonate or copolycarbonate, characterized in that the polycarbonate or copolycarbonate also comprises one or more specific additives.
Extruded foils composed of polycarbonate, polyester carbonate or else blends composed of PC and of polyesters, such as polyethylene terephthalates, polybutylene terephthalates or polycyclohexanedimethanol cyclohexanedicarboxylate (PCCD) are used especially in the electronics sector, for decorative and functional panels in the domestic-equipment sector, as topcoat foils, e.g. for sports items, and for ID cards and blister packs, examples of trademarks being Lexan SLX® and XYLEX® (both from Sabic Innovative Plastic). Further application sectors are found in the automobile construction sector, examples being bodywork parts or exterior mirrors, or in the telecommunications sector, an example being mobile-telephone casings and mobile-telephone keypads. The foils feature high transparency, impact resistance and heat resistance.
One particular sector that uses substrate materials for the production of foils is that of portable data carriers. There are many applications that use portable data carriers, in a very wide variety of embodiments. The portable data carriers here often have an inscription, or have security features incorporated, or have a magnetic strip and/or an integrated circuit. In particular, the portable data carriers can have been designed as plastics cards with standard dimensions, and can be used by way of example for cashless-payment transactions, or as proof of authority for access to a mobile-telephone network, etc. There are also known portable data carriers generally integrated as a page in a passbook and generally having lower thickness but larger area than standard plastics cards.
Because portable data carriers are widely used, another increasingly important factor, alongside production costs, is the environmental compatibility of the materials used. In most applications, another requirement is that the portable data carriers have a long lifetime. Furthermore, the portable data carriers are increasingly provided with inscriptions and add-on elements, with a simultaneous increase in the level of associated quality requirements.
One known process for the production of high-quality portable data carriers is lamination from a plurality of plastics foils. However, the production of complex-structure portable data carriers from a large number of individual foils is complicated and subject to severe restrictions in terms of selection of materials, in particular for adjacent individual foils. The individual foils moreover have to have a certain minimum thickness, to permit handling. Production of portable data carriers has therefore already switched to use of coextruded foils composed of a plurality of layers. During the process for producing these materials, the individual layers are bonded to give a multilayer foil. A plurality of the said multilayer foils can then be bonded to one another by lamination.
This type of procedure is known by way of example from EP-A 0 640 940, which discloses a contactless chip card having a core foil arranged between two topfoils. Each of the topfoils has been bonded by means of a bonding layer to the core foil. Each bonding layer has in particular been designed as a layer coextruded with the topfoils and/or with the core foil. The topfoils and the core foil are composed by way of example of polycarbonate. The bonding layers can be composed of a modified polyester termed PETG.
U.S. Pat. No. 5,928,788 discloses inter alia a multilayer data carrier, produced via lamination of a core foil and of two topfoils. The core foil and the topfoils are in particular composed of PETG. In order to prevent excessive adhesion to the plates of the laminating press, the outer region of the topfoils has an increased concentration of “antiblock” substances. To this end, each of the topfoils is coextruded from two layers, but only one of these layers comprises the antiblock substances.
WO 2002/41245 A2 discloses a multifunctional card body formed from a plurality of foils bonded to one another via lamination, where at least one foil is composed of at least two coextruded layers. In particular, a core foil has been bonded bilaterally in each case to a topfoil. Each of the topfoils can have been designed as a coextruded polycarbonate foil with two or three coextruded layers. The core foil can have two different types of coextruded layers. The two types of coextruded layers follow each other in alternation, and one layer structure here is formed from three or five alternating coextruded layers. One type of coextruded layer can be composed of polycarbonate or polyethylene terephthalate (PET). The other type of coextruded layer can be composed of a thermoplastic elastomer.
EP-A 0 706 152 discloses laminated chip cards or smart cards composed of thermoplastic materials. The said composite produced from laminatable foils has marked advantages over cards produced via a complicated adhesion process, e.g. by means of cyanoacrylate adhesives.
Polycarbonate is particularly suitable for the foils described above, because of its good mechanical properties.
Polycarbonates with additives from the class of the mould-release agents have been described by way of example in WO 99/05205 A or U.S. Pat. No. 6,008,280. These polycarbonates are used by way of example as substrate materials for optical data carriers, since these materials have better processing properties in the injection-moulding process. However, there is no description of card applications as described above, or lamination properties, of polycarbonates thus modified.
DE 10 2007 004 332 discloses multilayer composite materials comprising at least one layer of polycarbonate, optionally comprising mould-release agent, for example pentaerythritol tetrastearate and glycerol monostearate, preferably in an amount of from 0.02 to 1% by weight. Both of the compounds mentioned are within the group of additives 1-8 according to the invention. The usual function of mould-release agents is, as the name indicates, to act as release agents. As such, the said agents are known to have relatively good adhesion-inhibiting properties. It is not therefore possible to conclude from the cited document that the mould-release agents mentioned, in relatively high concentrations, have adhesion-improving properties.
The finished card body or multilayer composite material is in particular produced via a lamination press, in which the foil bundle is intimately bonded with exposure to pressure. It is advantageous here if at least one of the core foils or of the topfoils has a very favourable tendency towards adhesion during the lamination process. The result can be an accelerated process of producing the said foil composites. Furthermore, there is an improvement in the adhesion of the topfoils on the core foil. The said core foil can be a transparent and/or coloured foil, and can have good mechanical properties. The topfoils can moreover be laser-printable. It is therefore preferable here to use polycarbonate.
However, foils composed of polycarbonate have the disadvantage of a high processing temperature in the lamination process. Furthermore, a prolonged period is needed for lamination of the foils. The result is prolongation of the lamination cycles described above, and a requirement for long production times. Delamination can also occur during use of the finished foil laminate, because of inadequate adhesion between the foils.